DnaK-dependent ribosome biogenesis in Escherichia coli: competition for dominance between the alleles dnaK756 and dnaK+.

The Escherichia coli chaperone DnaK is vital for many cellular functions, including ribosome biogenesis at high temperature. Thus, the dnaK756-ts (lambdaR) mutant, at the non-permissive temperature, is inhibited at a late stage of ribosome assembly, yielding 21S, 32S and 45S precursor particles. This defect, unlike the lambda resistance and thermosensitivity phenotypes, is not complemented by lysogenisation with a transducing phage lambda dnaK+ bearing the wild-type dnaK gene. However this dominant phenotype becomes recessive when dnaK+ is expressed from a medium-copy-number plasmid. On the other hand, an excess of DnaK causes an unexpected dominant-lethal effect of the dnaK756 allele near non-permissive temperatures. This interplay between the dnaK+ and dnaK756 alleles supports the idea of that DnaK oligomers form in the cell.